Plasmalemma and Tonoplast Influxes of Potassium in Barley Roots, and Interpretation of the Absorption Isotherm at High Concentrations

1975 ◽  
Vol 2 (2) ◽  
pp. 177 ◽  
Author(s):  
JB Robinson ◽  
GG Laties
Keyword(s):  
Steady State ◽  
High Concentration ◽  
Experimental Conditions ◽  
Apparent Increase ◽  
Absorption Isotherm ◽  
Low Salt ◽  
High Concentrations ◽  
High Concentration Range ◽  
Kinetics Of ◽  
Potassium Exchange

Estimates of plasmalemma influx and steady-state vacuolar influx of potassium in low-salt barley roots have been obtained in the concentration range 10-80 mM by the use of controlled loading and washing times. Both fluxes are reduced by preloading the tissue in solutions containing potassium. When the experimental temperature is increased from 20 to 30°C, an apparent increase in the steady-state vacuolar influx occurs; separation of this flux from the apparent plasmalemma influx is not possible. The data support the hypothesis that the kinetics of potassium exchange in barley root tissue may be confounded by both loading time and temperature, and thus interpretation of the influx isotherm in the high concentration range is difficult. Where experiments are carried out at 20-25°C the steady- state vacuolar influx is measured unless closely defined experimental conditions obtain. At higher temperatures the plasmalemma influx may be measured.

scholarly journals A model of bubble coalescence in the presence of a nonionic surfactant with a low bubble approach velocity

2021 ◽  
Author(s):  
Yuelin Wang ◽  
Huahai Zhang ◽  
Tiefeng Wang
Keyword(s):  
Nonionic Surfactant ◽  
Surfactant Concentration ◽  
Bubble Coalescence ◽  
Bulk Concentration ◽  
High Concentration ◽  
Coalescence Time ◽  
Approach Velocity ◽  
Marangoni Stress ◽  
High Concentrations ◽  
High Concentration Range

A bubble coalescence model for a solution with a nonionic surfactant and with a small bubble approach velocity was developed, in which the mechanism of how coalescence is hindered by Marangoni stress was quantitatively analyzed. The bubble coalescence time calculated for ethanol-water and MIBC-water systems were in good agreement with experimental data. At low surfactant concentrations, the Marangoni stress and bubble coalescence time increased with bulk concentration increase. Conversely, in the high concentration range, the Marangoni stress and coalescence time decreased with bulk concentration. Numerical results showed that the nonlinear relationship between coalescence time and surfactant concentration is determined by the mass transport flux between the film and its interface, which tends to diminish the spatial concentration variation of the interface, i.e., it acts as a “damper”. This damping effect increases with increased surfactant concentration, therefore decreasing the coalescence time at high concentrations.

Time course and kinetics of proximal tubular processing of insulin

1992 ◽  
Vol 262 (5) ◽  
pp. F813-F822 ◽  
Author(s):  
S. Nielsen
Keyword(s):  
Steady State ◽  
Time Course ◽  
Accumulation Rate ◽  
Compartmental Analysis ◽  
Proximal Tubules ◽  
Hydrolysis Rate ◽  
Time Courses ◽  
High Concentrations ◽  
Kinetics Of

The present study was undertaken to determine the time courses and kinetics of the subcellular processing of 125I-insulin in isolated and in vitro perfused proximal tubules. Morphometric analysis demonstrated well-preserved ultrastructure after 90 min of perfusion. After luminal perfusion for 90 min the absorption was constant with time and reached steady state within 5 min (177 +/- 7 fg.min-1.mm-1). Also the hydrolysis rate and tubular accumulation rate were constant and averaged 84 +/- 8 and 93 +/- 10 fg.min-1.mm-1, respectively. Free 125I appeared already within 5 min of perfusion and reached steady state within 10 min. From proximal tubules perfused with 125I-insulin for 30 min and chased for 60 min, a compartmental analysis revealed two compartments; half time (t1/2) for delivery of insulin to the lysosomes was determined to be 8.5 min, and t1/2 for lysosomal degradation was 72 min. The results demonstrated that internalization by endocytic invaginations, incorporation in endocytic vacuoles, fusion with lysosomes, and hydrolysis were rapid processes and reached maximum rates within few minutes. A significant transtubular transport of insulin to the peritubular compartment was determined to be a constant rate of 11.2 +/- 0.7 fg.min-1.mm-1. Perfusion of tubules with insulin at high concentrations in the perfusate revealed that the transport was dependent on the absorbed amount and not on the perfused load, compatible with transport through the cells and not via a paracellular mechanism. The intactness of the tight junctions was supported by the following: 1) [14C]inulin leak did not increase with time and 2) enzyme-free intercellular spaces were evident after perfusion for only 5 min with microperoxidase (mol wt of 1,700). The transported 125I-insulin was trichloroacetic acid precipitable and immunoprecipitable.

Using lithium to probe sequential cation interactions with GAT1

2012 ◽  
Vol 302 (11) ◽  
pp. C1661-C1675 ◽  
Author(s):  
Anne-Kristine Meinild ◽  
Ian C. Forster
Keyword(s):  
Steady State ◽  
Binding Site ◽  
Voltage Dependence ◽  
Cation Binding ◽  
Experimental Conditions ◽  
Net Charge ◽  
Cation Binding Site ◽  
Voltage Dependent ◽  
Experimental Findings ◽  
Kinetics Of

Li+ interacts with the Na+/Cl−-dependent GABA transporter, GAT1, under two conditions: in the absence of Na+ it induces a voltage-dependent leak current; in the presence of Na+ and GABA, Li+ stimulates GABA-induced steady-state currents. The amino acids directly involved in the interaction with the Na+ and Li+ ions at the so-called “ Na2” binding site have been identified, but how Li+ affects the kinetics of GABA cotransport has not been fully explored. We expressed GAT1 in Xenopus oocytes and applied the two-electrode voltage clamp and 22Na uptake assays to determine coupling ratios and steady-state and presteady-state kinetics under experimental conditions in which extracellular Na+ was partially substituted by Li+. Three novel findings are: 1) Li+ reduced the coupling ratio between Na+ and net charge translocated during GABA cotransport; 2) Li+ increased the apparent Na+ affinity without changing its voltage dependence; 3) Li+ altered the voltage dependence of presteady-state relaxations in the absence of GABA. We propose an ordered binding scheme for cotransport in which either a Na+ or Li+ ion can bind at the putative first cation binding site ( Na2). This is followed by the cooperative binding of the second Na+ ion at the second cation binding site ( Na1) and then binding of GABA. With Li+ bound to Na2, the second Na+ ion binds more readily GAT1, and despite a lower apparent GABA affinity, the translocation rate of the fully loaded carrier is not reduced. Numerical simulations using a nonrapid equilibrium model fully recapitulated our experimental findings.

Study of kinetics of degradation of cyclohexane carboxylic acid by acclimated activated sludge

2016 ◽  
Vol 73 (10) ◽  
pp. 2552-2558 ◽  
Author(s):  
Chunhua Wang ◽  
Shuian Shi ◽  
Hongyan Chen
Keyword(s):  
Carboxylic Acid ◽  
Activated Sludge ◽  
Degradation Kinetics ◽  
Experimental Conditions ◽  
First Order Kinetics ◽  
Effects Of Ph ◽  
High Concentrations ◽  
Cyclohexane Carboxylic Acid ◽  
Kinetics Of ◽  
Acclimated Activated Sludge

Activated sludge contains complex microorganisms, which are highly effective biodegrading agents. In this study, the kinetics of biodegradation of cyclohexane carboxylic acid (CHCA) by an acclimated aerobic activated sludge were investigated. The results showed that after 180 days of acclimation, the activated sludge could steadily degrade >90% of the CHCA in 120 h. The degradation of CHCA by the acclimated activated sludge could be modeled using a first-order kinetics equation. The equations for the degradation kinetics for different initial CHCA concentrations were also obtained. The kinetics constant, kd, decreased with an increase in the CHCA concentration, indicating that, at high concentrations, CHCA had an inhibiting effect on the microorganisms in the activated sludge. The effects of pH on the degradation kinetics of CHCA were also investigated. The results showed that a pH of 10 afforded the highest degradation rate, indicating that basic conditions significantly promoted the degradation of CHCA. Moreover, it was found that the degradation efficiency for CHCA increased with an increase in temperature and concentration of dissolved oxygen under the experimental conditions.

scholarly journals Steady-state kinetics of catecholamine transport by chromaffin-granule ‘ghosts’

1974 ◽  
Vol 144 (2) ◽  
pp. 319-325 ◽  
Author(s):  
J H Phillips
Keyword(s):  
Steady State ◽  
Competitive Inhibitor ◽  
Affinity Constant ◽  
Chromaffin Granule ◽  
Affinity Constants ◽  
Steady State Kinetics ◽  
Low Concentrations ◽  
High Concentrations ◽  
Chromaffin Granule Ghosts ◽  
Kinetics Of

Resealed chromaffin-granule ‘ghosts’ were used to study the steady-state kinetics of catecholamine transport. The pump has a high affinity for (-)-noradrenaline, (-)-adrenaline, tyramine and 5-hydroxytryptamine (serotonin), but a lower affinity for (+)-noradrenaline. The measured rates of incorporation do not conform to Michaelis–Menten kinetics, but affinity constants for the former substrates are in the range 8–18μm. Reserpine is a potent inhibitor. Incorporation as a function of ATP concentration also fails to show simple kinetics; the affinity constant for ATP is deduced to be about 3mm at 1mm-MgCl2. Adenylyl (βγ-methylene)diphosphonate is a competitive inhibitor at low concentrations, but inhibits more strongly at high concentrations. The pump has a transition temperature at 29°C and does not seem to be identical with the Mg2+-stimulated adenosine triphosphatase of chromaffin granules.

scholarly journals Regulatory effects of ATP and luciferin on firefly luciferase activity

1995 ◽  
Vol 305 (3) ◽  
pp. 929-933 ◽  
Author(s):  
N Lembert ◽  
L Å Idahl
Keyword(s):  
Steady State ◽  
Active Site ◽  
Luciferase Activity ◽  
Firefly Luciferase ◽  
Kinetic Properties ◽  
Allosteric Site ◽  
Experimental Conditions ◽  
Regulatory Effects ◽  
High Concentrations ◽  
Firefly Luciferase Activity

ATP and luciferin are not only substrates of firefly luciferase, but can, in addition, modulate its activity. High concentrations of luciferin induce a conformational change of the enzyme that temporarily reduces the catalytic rate. Re-activation takes approx. 20 min and is independent of variation in the concentration of enzyme or ATP, but lengthens with increasing luciferin concentration. High concentrations of albumin reduce this luciferin effect. The kinetic properties of firefly luciferase determined from initial rates and at steady state after 1 min of catalysis have been analysed according to Michaelis-Menten kinetics. There is only one active site for each of the substrates. At steady state the Km and Vmax. values for both substrates are reduced in an uncompetitive manner. Hyperbolic Lineweaver-Burk plots indicate an activation by ATP probably by binding to an allosteric site. A model is presented which incorporates luciferin induced de- and re-activation effects. Experimental conditions to avoid the regulatory effects of substrates during ATP monitoring are proposed.

The effects of light quality and non-steady-state, localized 14CO2 pulse labeling on net assimilation and 14C translocation profiles in Heracleum lanatum

1976 ◽  
Vol 54 (11) ◽  
pp. 1206-1213 ◽  
Author(s):  
John Hoddinott ◽  
Paul R. Gorham
Keyword(s):  
Steady State ◽  
Light Quality ◽  
Diffusion Resistance ◽  
High Concentration ◽  
Steady State Kinetics ◽  
Small Spot ◽  
Net Assimilation ◽  
Heracleum Lanatum ◽  
Kinetics Of ◽  
Spot Tag

Red, green, blue, and white light of equivalent intensities of photosynthetically active radiation (PAR) (400–700 nm) had no effect upon leaf diffusion resistance, net assimilation, or translocation of leaves of Heracleum lanatum Michx. at 20 °C. Regardless of light quality at 80 μE m−2 s−1 PAR, 5 min and 40 min after the start of a 2-min application of 70 μCi of 14CO2 to a 1.33-cm2 spot on a leaflet, the major ethanol-soluble labeled assimilates were sucrose and glutamic acid while sucrose was the only labeled translocate. Regardless of light quality at 80 μE m−2 s−1 PAR, 5 min after the start of a 2-min spot tag, well defined ‘wave-like’ translocation profiles consisting of five peaks, 3 to 6 cm apart, were observed along 20 cm of petiole. Regardless of light quality, in 40-min experiments, the ‘wave-like’ profiles were replaced by typical, linear semilogarithmic translocation profiles. It is concluded that the initial ‘wave-like’ profiles were induced by perturbing the steady-state kinetics of synthesis and vein loading labeled sucrose by pulse labeling a small spot with an unusually high concentration of 14CO2. It is possible that pulsed profiles reported by others may have originated in similar fashion.

Alteration in the myosin phosphorylation pattern of smooth muscle by phorbol ester

1990 ◽  
Vol 259 (5) ◽  
pp. C769-C774 ◽  
Author(s):  
M. Seto ◽  
Y. Sasaki ◽  
Y. Sasaki
Keyword(s):  
Steady State ◽  
Light Chain ◽  
Myosin Light Chain ◽  
High Concentration ◽  
Tension Development ◽  
Aortic Artery ◽  
Phosphorylation Pattern ◽  
Mlc20 Phosphorylation ◽  
High Concentrations ◽  
The Relationship

Pretreatment with a high concentration of phorbol 12-myristate 13-acetate (PMA, 100 nM) increased the degree of tension and extent of myosin light chain (MLC20) phosphorylation in the K(+)-stimulated rabbit aortic artery. Pretreatment with 100 nM PMA did not alter the relationship between MLC20 phosphorylation and the tension seen with K+ stimulation in the initial phase and steady state of contraction. However, a low concentration of PMA (10 nM) potentiated only the MLC20 phosphorylation during the steady state of contraction with no effect on the tension. In contrast, the prostaglandin (PG) F2 alpha-induced tension development and the MLC20 phosphorylation were not affected by PMA pretreatment at both low and high concentrations. The inhibitory action of nifedipine on the K(+)-induced contraction was not affected by pretreatment with 100 nM PMA; the concentration producing half-maximal inhibition of nifedipine for the K(+)-induced contraction (33 nM) was the same as that of the K+ plus 100 nM PMA-induced contraction (32 nM). Our results suggest that PMA may increase the level of myosin light chain kinase-dependent MLC20 phosphorylation and the tension in the K(+)-stimulated artery, an effect which differs from that seen with increases in K+ concentrations. The regulatory mechanism for the contraction involving PGF2 alpha stimulation may differ from that seen in the case of K+ stimulation.

Kinetics of binding of cholecystokinin to pancreatic acini

1988 ◽  
Vol 255 (1) ◽  
pp. G106-G112
Author(s):  
S. A. Wank ◽  
R. T. Jensen ◽  
J. D. Gardner
Keyword(s):  
Steady State ◽  
Energy Metabolism ◽  
Binding Sites ◽  
Incubation Temperature ◽  
Potassium Thiocyanate ◽  
Experimental Conditions ◽  
Pancreatic Acini ◽  
Cellular Energy ◽  
Cellular Energy Metabolism ◽  
Kinetics Of

In the present study we examined the kinetics of binding of iodinated COOH-terminal octapeptide of cholecystokinin (125I-CCK-8) to its receptors on dispersed acini prepared from guinea pig pancreas. At 37 degrees C, binding of 125I-CCK-8 reached a steady state after 60 min of incubation. Dissociation of bound 125I-CCK-8 was biphasic, indicating that the labeled peptide binds in two distinct states: a rapidly dissociating state and a slowly dissociating state. Binding of 125I-CCK-8 in the rapidly dissociating state was maximal within 3 min of incubation, did not depend on incubation temperature or cellular energy metabolism, could be stripped by 0.5 M potassium thiocyanate, and showed accelerated dissociation with CCK-8 or dibutyrylguanosine 3',5'-cyclic monophosphate (Bt2cGMP). Binding of 125I-CCK-8 in the slowly dissociating state was maximal after 60 min of incubation, was decreased by reducing the incubation temperature or inhibiting cellular energy metabolism, was not stripped by 0.5 M potassium thiocyanate, and did not show accelerated dissociation with CCK-8 or Bt2cGMP. Increasing the concentration of 125I-CCK-8 increased the fraction of radioactivity bound in the rapidly dissociating state. When binding of 125I-CCK-8 reached a steady state, nearly all of the bound radioactivity was in the slowly dissociating state. Computer analysis of the inhibition of 125I-CCK-8 by CCK-8 under experimental conditions where the rapidly dissociating state predominates demonstrated a complete loss of high-affinity binding sites.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Biosorption of chromium and nickel from aqueous solution using pine cones, Eucalyptus bark, and moringa pods: a comparative study

2020 ◽  
Author(s):  
Mohammed Matouq ◽  
Moatasem Saleh ◽  
Omar Al-Ayed ◽  
Tayel El-Hasan ◽  
Yamada Hiroshi ◽  
...  
Keyword(s):  
Heavy Metals ◽  
Removal Efficiency ◽  
Order Kinetic ◽  
Adsorption Model ◽  
High Concentration ◽  
Experimental Conditions ◽  
Removal Capacity ◽  
Pine Cones ◽  
Kinetics Of ◽  
Eucalyptus Bark

Abstract Low-cost local plants (Eucalyptus Bark, Moringa Pods, Pine cones) have been successfully used to remove heavy metals from simulated wastewater. Two types of heavy metals were chosen to study the removal capacity, Nickel (Ni) and Chrome (Cr), with a concentration of 400, 600, 900 ppm. The results show that Moringa pods have the best removal capacity for heavy metals with percentages of 90–99% for both metals, Ni and Cr, for the Eucalyptus Bark the removal capacity percentages reach 50–98%, while for the pine cones revealed a lower removing capacity with percentages of 40–99%, indicating that this is the lowest removal capacity. The data has been best fitted to the Langmuir adsorption model for all plants, while the Freundlich adsorption model could not fit the obtained results at the experimental conditions. The kinetic study has revealed that the first-order kinetic model successfully describes the kinetics of Ni adsorption, while the second-order describes the kinetics of Cr adsorption. The removal of heavy metals (Ni, Cr) was obtained when moringa was used; its highest removal efficiency was reached within 20 minutes. On the other hand, other plants (Eucalyptus Bark, Pine cone) removal efficiency was attained in more than two hours. The removal is remarkable even at a high concentration of heavy metals, especially with the moringa plant.

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